digit = ord(char) - ord('0')

digit = ord(char) - ord('0')
if digit > 9 then digit -= 7

public static int parseInt(String s, int radix)
    throws NumberFormatException
{
    if (s == null) {
        throw new NumberFormatException("null");
    }

if (radix < Character.MIN_RADIX) {
    throw new NumberFormatException("radix " + radix +
                    " less than Character.MIN_RADIX");
}

if (radix > Character.MAX_RADIX) {
    throw new NumberFormatException("radix " + radix +
                    " greater than Character.MAX_RADIX");
}

int result = 0;
boolean negative = false;
int i = 0, max = s.length();
int limit;
int multmin;
int digit;

if (max > 0) {
    if (s.charAt(0) == '-') {
    negative = true;
    limit = Integer.MIN_VALUE;
    i++;
    } else {
    limit = -Integer.MAX_VALUE;
    }
    multmin = limit / radix;
    if (i < max) {
    digit = Character.digit(s.charAt(i++),radix);
    if (digit < 0) {
        throw NumberFormatException.forInputString(s);
    } else {
        result = -digit;
    }
    }
    while (i < max) {
    // Accumulating negatively avoids surprises near MAX_VALUE
    digit = Character.digit(s.charAt(i++),radix);
    if (digit < 0) {
        throw NumberFormatException.forInputString(s);
    }
    if (result < multmin) {
        throw NumberFormatException.forInputString(s);
    }
    result *= radix;
    if (result < limit + digit) {
        throw NumberFormatException.forInputString(s);
    }
    result -= digit;
    }
} else {
    throw NumberFormatException.forInputString(s);
}
if (negative) {
    if (i > 1) {
    return result;
    } else {    /* Only got "-" */
    throw NumberFormatException.forInputString(s);
    }
} else {
    return -result;
}
}

public class StringToInt {

    public int ConvertStringToInt(String s) throws NumberFormatException
    {
        int num =0;
        for(int i =0; i<s.length();i++)
        {
            if(((int)s.charAt(i)>=48)&&((int)s.charAt(i)<=59))
            {
                num = num*10+ ((int)s.charAt(i)-48);
            }
            else
            {
                throw new NumberFormatException();
            }

        }
        return num;
    }

    public static void main(String[]args)
    {
        StringToInt obj = new StringToInt();
        int i = obj.ConvertStringToInt("1234123");
        System.out.println(i);
    }

}

public static int parseInteger(String stringNumber) {
    int sum=0;
    int position=1;
    for (int i = stringNumber.length()-1; i >= 0 ; i--) {
       int number=stringNumber.charAt(i) - '0';
       sum+=number*position;
       position=position*10;

    }
    return sum;
}

int convertStringtoInt(String number){

    int total =0;
    double multiplier = Math.pow(10, number.length()-1);
        for(int i=0;i<number.length();i++){

            total = total + (int)multiplier*((int)number.charAt(i) -48);
            multiplier/=10;

        }

        return total;
    }